That money could have helped to prevent a Manchester attack or a murderous rampage on London Bridge.

But the argument you hear from senior defence officials in Portsmouth, is that the future is an uncertain space and so the UK needs this big hulk of grey metal to act as an insurance policy against all manner of unforeseen threats.

Some of those threats we can predict: Russia, North Korea, a rogue state or an insurgent group which can be attacked from the mobile platform that this
aircraft carrier will provide.

Some of those threats are yet to rear their heads and are yet to be identified.

Both the Defence Secretary and the First Sea Lord told me on Thursday that HMS Queen Elizabeth – and HMS Prince of Wales - will provide the UK with an adaptable, flexible defence resource for many decades to come.

Workmen putting the finishing touches. Credit: PA

But an aircraft carrier needs both aircraft and a working escort of naval destroyers. Right now, it has neither.

No one can guarantee the full order of F-35 fighter jets. The UK had initially intended to buy more than 130 of the new generation planes – many of which will fly from this carrier. It might now order only half that amount.

And the Royal Navy destroyers, which are required to sail with and protect any aircraft carrier, are currently beset with mechanical problems.

Admiral Sir Philip Jones, the most senior naval officer, admitted that the engines on the new Type 45 Destroyers “have given us some challenges in the past few years”.

It proves that investment decisions in one area of UK defence can be severely offset by poor decisions elsewhere.